In October 2010, as heavy smog hung over Beijing, the U.S. embassy’s Twitter feed said its rooftop pollution sensor had detected “crazy bad” levels of hazardous microparticles. So-called PM2.5 had shot up to about 550 micrograms per cubic meter—a level to which programmers had given the sardonic label because they thought it would never be reached. …

By now, rooftop sensors like those that drew attention to Beijing’s pollution sprout from 26 diplomatic posts in 16 countries. Their immediate goal is to protect the health of U.S. diplomats. But they are raising concerns about air pollution from Sarajevo to New Delhi and supplying data to research efforts. The “little-air-monitor-that-could,” as physicist and former U.S. diplomat David Roberts calls it, has become a worldwide watchdog. …

Findings are radiating into other disciplines. During a stint at the U.S. consulate in São Paulo, Brazil, Tommy Flynn, a program manager with the South Carolina Department of Health and Environmental Control, is providing technical assistance on the monitors.

The National Health Security Preparedness Index shows that overall, the United States’ day-to-day readiness for managing a public health crisis last year improved by 11 percent since the index’s first iteration in 2013, scoring a 7.1 on a 10-point scale. Thirty-eight states and the District of Columbia also boosted their overall health security in the last year, with Maryland scoring an 8.0 to outpace all other states.

“Threats to America’s health security are on the rise, but so is our nation’s preparedness to deal with these emergencies,” Dr. Alonzo Plough, chief science officer at the Robert Wood Johnson Foundation, said in a press release. “The Index shows how prepared public and private stakeholders are to tackle health security challenges and sheds light on areas for improvement.”